How many
yellow-eyed penguins on Rakiura?
In November 1999, the Yellow-eyed Penguin Trust started a survey of Yellow-eyed
penguin numbers on Stewart Island (Rakiura). Yellow-eyed penguin numbers
on the island have never been systematically counted and estimates have
ranged between 470 and 600 breeding pairs. In an effort to provide the
Yellow-eyed Penguin Species Recovery Group with a more accurate figure,
the Trust started a survey of the Island.

The survey took place over three field seasons. In the 1999 season, the
north-eastern coast of the island was covered, in the 2000 season the
west and south-eastern coasts were covered and finally in 2001 adjacent
Whenua Hou/Codfish Island was completed.

The project and the fieldwork was lead by David Blair, the projects officer
for the Yellow-eyed Penguin Trust. He was joined by a number of volunteers,
including Department of Conservation staff who took annual leave in order
to assist. The fieldwork was also supported by the Departments Southern
Islands, Stewart Island and Coastal Otago Field Centres who assisted with
logistics and provided boats. Searchers were accommodated in tents and
huts and in the first season on David Blairs boat Irene.

The search
All areas of known and former yellow-eyed penguin habitat were searched,
as were those areas that were considered suitable habitat. Some areas
of the Stewart Island coast are cliff-bound and without suitable penguin
landing sites and these areas were not searched. Suitable areas were checked
for sign of yellow-eyed penguins - tracks on beaches, penguin paths and
penguin poo. In some areas, the coastline was cruised along in the late
afternoon when penguins are often seen standing on their landings.

Once sites had been identified the real work started. Penguin paths were
followed through the bush and scrub in an effort to find nests. This was
often an exersize in frustration as paths took tortous routes and often
petered out into a roost site. The area had to be throughly searched and
every possible path followed. Once the nest sites were found, the location
was recorded using a Global Positioning System (GPS), the nest details
recorded and the nest physically marked so that others in the party did
not "rediscover" the nest. Sometimes nest searches were productive
with several being found but on average in took 2 hours of searching time
to find each nest.

Results
A mere 79 nests were found on the Stewart Island mainland, a further 38
on adjacent islands and 61 on Whenua Hou/Codfish island. The total of
178 breeding pairs was far short of the 470-600 previously estimated.
A clue as to why this figure should be so low is that 99 breeding pairs
were found on offshore islands. Although these islands comprise a small
percentage of available habitat they hold the majority of the breeding
population. It was also observed that very few juvenile (1 year-old) penguins
were seen on the mainland, where as on cat-free Whenua Hou numerous juveniles
were seen.

The culprit would seem to be the domestic cat. Wild cats may be found
throughout Stewart Island and have been implicated in the decline of other
birdlife there. Fortunately, they are restricted to the main island and
islands such as Whenua Hou remain predator-free.

What now?
Although cats may be to blame, further work is needed to rule out other
factors, such as food availability. Removing wild cats from Stewart Island
would outwardly seem to be a good, but difficult and expensive idea. However
given that the primary diet of the cats is rats, the demise of cats may
increase the rat predation problems of other vulnerable species.

What we can do is guard our islands from the arrival of predators and
to carefully work out how to best protect the penguins on the mainland.

Update
Since 2001 work has been ongoing to try and understand the Stewart Island problem. The Department of Conservation undertook a cat control operation in the northern part of Stewart Island while the Yellow-eyed Penguin Trust undertook monitoring of penguin nests. Unfortunately most of the chicks died of unknown causes before the end of the guard stage, before we expected them to be most vulnerable to cats. Several causes of mortality in young chicks have been
identified including a Corynebacterium (or avian diphtheria) infection that killed 50% of South Island chicks in 2004, a Leucocytozoonblood parasite previously only known from Fiordland penguins and chick starvation. All of these are currently under study with Massey University investigating disease issues and the Yellow-eyed Pengin trust and Otago University investigating penguin foraging and diet. Follow the work here >>>